In the event of a frontal collision of a vehicle against a rigid barrier (hereinafter referred to as a barrier), the kinetic energy is absorbed by effectively deforming a chassis frame that hits the barrier, so that a survival space can be secured and the safety of the occupants can be thus improved.
JP-A-2000-203451 discloses a structure in which inner reinforcements are fixed respectively to a pair of side-member bodies which extend in a front-to-rear direction and each of which has an inflecting portion formed in a middle portion thereof. Each of the inner reinforcements has a variable cross-sectional structure which provides approximately uniform cross-sectional stiffness to the corresponding side-member body.    Patent Document 1: JP-A-2000-203451